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MG MGB Technical - Tappet push rod differences. 18GK and 18V

I have an 18GK series engine with one push rod longer than all the others. Is it possible that maybe the PO replaced a valve and used a tappet and push rod from an 18V series engine. It seems to work, but has me worried that maybe the cam lobe was so badly worn that a longer push rod was installed to counteract the problem. I see that Moss has a different part number for the 18 GK and 18V engines tappet/push rod.
G Nicholas

Early engines have a longer and heavier tappet and a shorter pushrod than the later 18V types.. Either type can be used as the overall length of each set is the same.The later type is preferable , anything which reduces weight in the valve train is benificial especially if you use higher revs, tho for normal road use you are unlikely to notice the difference.

Jim
jim soutar

Measure the longer pushrod. If it is 10.656” (270.662mm) long, then it's from an 18V engine.
Steve S.

I have a similar problem. I am fitting a new cam in my 68B engine fitted a set of 18V type APT lifters and country 18v push rods. The push rods are a lot too short they measure 269mm ball to top of the cup. The measurement Steve gives would be close. The numbers on the box are :Type-CPR-5. I have ordered a set of tube ones made up. I wonder what the ones I have are for. The base dia. of the cam is a little less than stock and I measure that I need 5mm longer than these country ones. Steve how does the configuration work out with the 18V bits with the early engine? Thanks.
Denis
Denis4

Providing you use the later tappets and pushrods they are compatible with the early block. The range of adjustment on the rockers should be adequate to cope with any reduction in base circle of the cam. Just checked a set of 18v push rods and they are the same as yours Jim
jim soutar

Denis-
Going by your description of the lobe, you have a regrind profile. The 18V engines use cylinder heads that have a shorter height (3.125” / 79.4mm) than the earlier cylinder heads of the 18G-18GK engines (3.172” / 80.6mm, so the total length of the tappet / pushrod assembly is slightly different. Fortunately, when using a camshaft with the an Original Equipment base circle diameter (a.k.a. "heel" diameter), the difference can be taken up by the adjuster on the rocker arm. A regrind profile has a smaller base circle diameter, so usually a custom-length pushrod is needed.
Steve S.

Steve this is a billet cam by a local cam grinder here in OZ for use with a supercharger. His answer when I asked about the reduction in base circle was that with the higher lobe lift the tip of the lobe would be higher than the cam bearing area and not fit into the engine. I went for the new cam in the first place to keep the base circle close to standard. The cam lift is 045" over standard. In the mean time I had fitted the cam and cant check the measurements. The one advantage now is that the new push rods will be a lot lighter than the standard 18V. Thanks for the help, Denis
Denis4

This thread was discussed between 06/06/2009 and 08/06/2009

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